The present invention relates to vehicle braking systems and, in particular, to an apparatus and method for isolating an intact portion of a service braking circuit from a failed service brake wheel end. Additionally, the present invention isolates a failed parking brake from an intact portion of a parking brake circuit. By isolating the failed service brakes and parking brakes of a vehicle from the rest of the braking system, complete immobilization of the vehicle can be prevented while maintaining use of the antilock braking system (ABS) in the event of a wheel end failure.
The present invention protects the intact wheel ends of a service braking circuit from a failure of a portion of the failed circuit. The operation state of the parking brake of each wheel end may be determined by monitoring air line pressure, force applied to the wheel end, wheel speed, temperature at the wheel end, and/or other like parameters. When a failed wheel end is detected, the remaining intact wheel ends' service brake control is protected and isolated from the failed wheel end.
Moreover, it is desirable to maintain use of the ABS in the event of a service brake failure. With rear axle wheel end failures, for example, braking systems often revert to spring brake modulation, but this eliminates antilock braking on all wheel ends of the affected braking circuit. The present invention, however, allows for ABS control on the intact wheel ends of a braking circuit with a failed wheel end. Further, the present invention allows for more system pressure to be retained with the failed wheel end by isolating the failed pneumatic wheel end from the intact portion of the pneumatic braking system.
In accordance with an exemplary embodiment of the present invention, an antilock braking system control unit is used to control individual service-braked wheel ends by using ABS modulators as isolation devices. Many different parameters can be used to sense individual parking brake status, such as air line pressure, wheel speed, stroke, torque, wheel slip, temperature and the like. In particular, it is desirable to use park line pressure to isolate the pressure to the service side of the failed wheel end.
As an alternative to the above-described electronic control embodiment, a pneumatic control or an electro-pneumatic control can be used to control the braking system. In particular, pneumatic isolation valves can be used to isolate the service brake side of the system.
With regard to parking brakes, commercial vehicles are typically equipped with spring-actuated/fluid released parking brake systems, in particular pneumatic systems which utilize compressed air to release the parking brake actuator of each wheel end's spring brake actuator. The parking brakes in such vehicles remain released as long as the parking brake release pressure is maintained in spring brake actuators. Such systems typically have a common source of pressure connected to each wheel end's spring brake actuator, such that application of pressure to the common lines simultaneously releases the vehicle's parking brakes.
A single point of failure in such systems may result in application of all of the wheel end spring applied parking brake portions of the parking brake actuators, effectively immobilizing the vehicle. For example, in a typical 6×4 vehicle, a rupture of any one of the four pneumatic lines to the wheel ends could result in parking brake release pressure being bled off from all four spring brake actuators. This has been the standard industry design practice, as a failure of a single brake actuator or the pressure delivery to a single axle has been viewed as a serious event warranting automatic full application of all of the vehicle's brakes as desirable “fail safe” outcome.
Notwithstanding the common industry design practice, there may also be situations in which full parking brake application and the resulting complete immobilization of the vehicle could have undesired consequences. For example, in a commercial application of a vehicle with multiple axles such as a logging truck, being forced to park or automatically immobilize the vehicle in the event of a parking brake release pressure failure at one wheel end may be highly undesirable when the vehicle is at a remote location (such as deep in a forest on a logging road), where repair facilities are far away and/or the immobilization of the vehicle may block a much-needed passage, such as a fire road in the case of a logging truck or the travel lanes of a high speed, high vehicle volume highway in the case of an over-the-road commercial vehicle.
Other examples where automatic application of all spring applied parking brakes in the event of a single wheel end failure may be undesirable include heavy police vehicles or military vehicles which may be subjected to combat conditions such as criminal attacks or exposure to improvised explosive devices (“IEDs”). During such an event, damage to a pneumatic line serving one wheel end in a prior art common-supply parking brake system could cause all of the wheel ends' parking brakes to be immediately applied, effectively immobilizing the vehicle in a location where the vehicle and its personnel would be vulnerable to further attacks.
It would be desirable to have a brake system which, in addition to permitting full parking brake release and application capability in normal operating conditions, also responds to a line failure at one wheel end in a manner which provides for continued reliable release and application of the parking brakes of the remaining undamaged wheel ends.
The present invention solves the above-described and other problems of the prior art by arranging devices at each wheel end which function as wheel end shut-off devices to isolate the damaged wheel end from the remaining portions of the service brake system and the parking brake system while not restricting flow during spring brake modulation.
The invention is not limited to damage affecting solely the lines between the flow control components and a parking brake actuator, but includes any damage at a wheel end which may result in the release of parking brake release pressure, such as damage to the parking brake release actuator portion of a wheel end's spring brake actuator.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.